Field of Invention
The field of the invention concerns machining devices and in particular those used for reaming, milling, boring and counter-boring of turbine shafts. The field of the invention relates to devices limiting the vibration induced during machining operations that comprise shaft reaming, milling, boring or counter-boring.
Description of Prior Art
At present, there exist different techniques permitting the reaming, boring and counter-boring of shafts. Such operations can be highly complex to master when the operation takes place on long shafts and must be carried out blind, i.e. without visibility of the operation carried out.
In particular, the tool permitting the machining must ensure the straightness of operation in order to guarantee a constant delta, i.e. to guarantee that the tolerances for the internal diameter of shafts is respected and without the presence of any undulations in order to respect dynamic operating criteria. Furthermore, it must ensure a machined diameter within a limited tolerance. In addition, the tool must guarantee balance and a regularity of the surface state obtained after machining.
Generally, for aircraft turbine-engine shafts, the orders of magnitude are a machined length of 2300 mm, with a delta of 0.01 mm and a straightness tolerance of 0.02 mm
At the present time, this calibration operation is carried out on a boring machine by a bar equipped with a calibration head on its end.
One problem noted is that the smaller the diameter of the shaft to be machined, the more vibration increases during machining. The vibration phenomenon generated by this type of machining corresponds to a relative movement, that between the part being machined and the cutting tool, this translates into more or less marked undulations of the machined surface.
The smaller the diameter of the tool bearing bar, the greater the amplitude of vibration is likely to increases.
In the case of deep counter-boring, taking into account the relationship between diameter and length, the vibration phenomenon is difficult to resolve. Various solutions exist, including for example:                the stiffening of the part using bezels in order to externally hold the shaft during rotary boring;        the choice of cutting tools with an optimisation of their cutting angle, steel grade or coverings;        an optimisation of the cutting parameters, such as rotation speed, the number of cutting edges, tool advance per rotation and an adjustment of the flowrate and pressure of the cutting fluid coolant.        
But such solutions are not completely satisfactory since they do not totally suppress the appearance of vibration. Furthermore, they can be complex and difficult to implement.